The present invention relates to a coupling device between a surface wave line and a microstrip line. More precisely it relates to a coupling device between a microstrip line, in which the field distribution is asymmetric, operating in quasi-TEM mode, and an access line to a device, such as an isolator or a non-reciprocal ferrite device, in which the field distribution is symmetric, using an electromagnetic surface mode propagating in a thin core line, charged with ferrite pieces, and biased by a magnetostatic field.
An object of the invention is to make this non reciprocal device integrable, and to omit the coaxial connectors which were used up to present, because they are too bulky for integration.
A known technique, giving satisfactory results but difficult to put into practice and so practically unusable consists in integrating, in the two access lines to the surface wave device, a coaxial line element in the form of a glass bead matched to 50 ohms, which is tantamount to reconstituting the system for exciting the electromagnetic surface wave mode used in known devices. However, this glass bead introduces parasitic elements disturbing the matching of the device.
Furthermore, experience has shown that direct connection of a microstrip line to the thin core line of a symmetrical surface wave device does not give good results, the insertion losses being too high.